roundtrip_js.go

// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

//go:build js && wasm

package req

import (
	"errors"
	"fmt"
	"io"
	"net/http"
	"strconv"
	"syscall/js"
)

var uint8Array = js.Global().Get("Uint8Array")

// jsFetchMode is a Request.Header map key that, if present,
// signals that the map entry is actually an option to the Fetch API mode setting.
// Valid values are: "cors", "no-cors", "same-origin", "navigate"
// The default is "same-origin".
//
// Reference: https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/fetch#Parameters
const jsFetchMode = "js.fetch:mode"

// jsFetchCreds is a Request.Header map key that, if present,
// signals that the map entry is actually an option to the Fetch API credentials setting.
// Valid values are: "omit", "same-origin", "include"
// The default is "same-origin".
//
// Reference: https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/fetch#Parameters
const jsFetchCreds = "js.fetch:credentials"

// jsFetchRedirect is a Request.Header map key that, if present,
// signals that the map entry is actually an option to the Fetch API redirect setting.
// Valid values are: "follow", "error", "manual"
// The default is "follow".
//
// Reference: https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/fetch#Parameters
const jsFetchRedirect = "js.fetch:redirect"

// jsFetchMissing will be true if the Fetch API is not present in
// the browser globals.
var jsFetchMissing = js.Global().Get("fetch").IsUndefined()

// jsFetchDisabled will be true if the "process" global is present.
// We use this as an indicator that we're running in Node.js. We
// want to disable the Fetch API in Node.js because it breaks
// our wasm tests. See https://go.dev/issue/57613 for more information.
var jsFetchDisabled = !js.Global().Get("process").IsUndefined()

// Determine whether the JS runtime supports streaming request bodies.
// Courtesy: https://developer.chrome.com/articles/fetch-streaming-requests/#feature-detection
func supportsPostRequestStreams() bool {
	requestOpt := js.Global().Get("Object").New()
	requestBody := js.Global().Get("ReadableStream").New()

	requestOpt.Set("method", "POST")
	requestOpt.Set("body", requestBody)

	// There is quite a dance required to define a getter if you do not have the { get property() { ... } }
	// syntax available. However, it is possible:
	// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/get#defining_a_getter_on_existing_objects_using_defineproperty
	duplexCalled := false
	duplexGetterObj := js.Global().Get("Object").New()
	duplexGetterFunc := js.FuncOf(func(this js.Value, args []js.Value) any {
		duplexCalled = true
		return "half"
	})
	defer duplexGetterFunc.Release()
	duplexGetterObj.Set("get", duplexGetterFunc)
	js.Global().Get("Object").Call("defineProperty", requestOpt, "duplex", duplexGetterObj)

	// Slight difference here between the aforementioned example: Non-browser-based runtimes
	// do not have a non-empty API Base URL (https://html.spec.whatwg.org/multipage/webappapis.html#api-base-url)
	// so we have to supply a valid URL here.
	requestObject := js.Global().Get("Request").New("https://www.example.org", requestOpt)

	hasContentTypeHeader := requestObject.Get("headers").Call("has", "Content-Type").Bool()

	return duplexCalled && !hasContentTypeHeader
}

// RoundTrip implements the RoundTripper interface using the WHATWG Fetch API.
func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
	// The Transport has a documented contract that states that if the DialContext or
	// DialTLSContext functions are set, they will be used to set up the connections.
	// If they aren't set then the documented contract is to use Dial or DialTLS, even
	// though they are deprecated. Therefore, if any of these are set, we should obey
	// the contract and dial using the regular round-trip instead. Otherwise, we'll try
	// to fall back on the Fetch API, unless it's not available.
	if t.DialContext != nil || t.DialTLSContext != nil || jsFetchMissing || jsFetchDisabled {
		return t.roundTrip(req)
	}

	ac := js.Global().Get("AbortController")
	if !ac.IsUndefined() {
		// Some browsers that support WASM don't necessarily support
		// the AbortController. See
		// https://developer.mozilla.org/en-US/docs/Web/API/AbortController#Browser_compatibility.
		ac = ac.New()
	}

	opt := js.Global().Get("Object").New()
	// See https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/fetch
	// for options available.
	opt.Set("method", req.Method)
	opt.Set("credentials", "same-origin")
	if h := req.Header.Get(jsFetchCreds); h != "" {
		opt.Set("credentials", h)
		req.Header.Del(jsFetchCreds)
	}
	if h := req.Header.Get(jsFetchMode); h != "" {
		opt.Set("mode", h)
		req.Header.Del(jsFetchMode)
	}
	if h := req.Header.Get(jsFetchRedirect); h != "" {
		opt.Set("redirect", h)
		req.Header.Del(jsFetchRedirect)
	}
	if !ac.IsUndefined() {
		opt.Set("signal", ac.Get("signal"))
	}
	headers := js.Global().Get("Headers").New()
	for key, values := range req.Header {
		for _, value := range values {
			headers.Call("append", key, value)
		}
	}
	opt.Set("headers", headers)

	var readableStreamStart, readableStreamPull, readableStreamCancel js.Func
	if req.Body != nil {
		if !supportsPostRequestStreams() {
			body, err := io.ReadAll(req.Body)
			if err != nil {
				req.Body.Close() // RoundTrip must always close the body, including on errors.
				return nil, err
			}
			if len(body) != 0 {
				buf := uint8Array.New(len(body))
				js.CopyBytesToJS(buf, body)
				opt.Set("body", buf)
			}
		} else {
			readableStreamCtorArg := js.Global().Get("Object").New()
			readableStreamCtorArg.Set("type", "bytes")
			readableStreamCtorArg.Set("autoAllocateChunkSize", t.writeBufferSize())

			readableStreamPull = js.FuncOf(func(this js.Value, args []js.Value) any {
				controller := args[0]
				byobRequest := controller.Get("byobRequest")
				if byobRequest.IsNull() {
					controller.Call("close")
				}

				byobRequestView := byobRequest.Get("view")

				bodyBuf := make([]byte, byobRequestView.Get("byteLength").Int())
				readBytes, readErr := io.ReadFull(req.Body, bodyBuf)
				if readBytes > 0 {
					buf := uint8Array.New(byobRequestView.Get("buffer"))
					js.CopyBytesToJS(buf, bodyBuf)
					byobRequest.Call("respond", readBytes)
				}

				if readErr == io.EOF || readErr == io.ErrUnexpectedEOF {
					controller.Call("close")
				} else if readErr != nil {
					readErrCauseObject := js.Global().Get("Object").New()
					readErrCauseObject.Set("cause", readErr.Error())
					readErr := js.Global().Get("Error").New("io.ReadFull failed while streaming POST body", readErrCauseObject)
					controller.Call("error", readErr)
				}
				// Note: This a return from the pull callback of the controller and *not* RoundTrip().
				return nil
			})
			readableStreamCtorArg.Set("pull", readableStreamPull)

			opt.Set("body", js.Global().Get("ReadableStream").New(readableStreamCtorArg))
			// There is a requirement from the WHATWG fetch standard that the duplex property of
			// the object given as the options argument to the fetch call be set to 'half'
			// when the body property of the same options object is a ReadableStream:
			// https://fetch.spec.whatwg.org/#dom-requestinit-duplex
			opt.Set("duplex", "half")
		}
	}

	fetchPromise := js.Global().Call("fetch", req.URL.String(), opt)
	var (
		respCh           = make(chan *http.Response, 1)
		errCh            = make(chan error, 1)
		success, failure js.Func
	)
	success = js.FuncOf(func(this js.Value, args []js.Value) any {
		success.Release()
		failure.Release()
		readableStreamCancel.Release()
		readableStreamPull.Release()
		readableStreamStart.Release()

		req.Body.Close()

		result := args[0]
		header := http.Header{}
		// https://developer.mozilla.org/en-US/docs/Web/API/Headers/entries
		headersIt := result.Get("headers").Call("entries")
		for {
			n := headersIt.Call("next")
			if n.Get("done").Bool() {
				break
			}
			pair := n.Get("value")
			key, value := pair.Index(0).String(), pair.Index(1).String()
			ck := http.CanonicalHeaderKey(key)
			header[ck] = append(header[ck], value)
		}

		contentLength := int64(0)
		clHeader := header.Get("Content-Length")
		switch {
		case clHeader != "":
			cl, err := strconv.ParseInt(clHeader, 10, 64)
			if err != nil {
				errCh <- fmt.Errorf("net/http: ill-formed Content-Length header: %v", err)
				return nil
			}
			if cl < 0 {
				// Content-Length values less than 0 are invalid.
				// See: https://datatracker.ietf.org/doc/html/rfc2616/#section-14.13
				errCh <- fmt.Errorf("net/http: invalid Content-Length header: %q", clHeader)
				return nil
			}
			contentLength = cl
		default:
			// If the response length is not declared, set it to -1.
			contentLength = -1
		}

		b := result.Get("body")
		var body io.ReadCloser
		// The body is undefined when the browser does not support streaming response bodies (Firefox),
		// and null in certain error cases, i.e. when the request is blocked because of CORS settings.
		if !b.IsUndefined() && !b.IsNull() {
			body = &streamReader{stream: b.Call("getReader")}
		} else {
			// Fall back to using ArrayBuffer
			// https://developer.mozilla.org/en-US/docs/Web/API/Body/arrayBuffer
			body = &arrayReader{arrayPromise: result.Call("arrayBuffer")}
		}

		code := result.Get("status").Int()
		respCh <- &http.Response{
			Status:        fmt.Sprintf("%d %s", code, http.StatusText(code)),
			StatusCode:    code,
			Header:        header,
			ContentLength: contentLength,
			Body:          body,
			Request:       req,
		}

		return nil
	})
	failure = js.FuncOf(func(this js.Value, args []js.Value) any {
		success.Release()
		failure.Release()
		readableStreamCancel.Release()
		readableStreamPull.Release()
		readableStreamStart.Release()

		req.Body.Close()

		err := args[0]
		// The error is a JS Error type
		// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error
		// We can use the toString() method to get a string representation of the error.
		errMsg := err.Call("toString").String()
		// Errors can optionally contain a cause.
		if cause := err.Get("cause"); !cause.IsUndefined() {
			// The exact type of the cause is not defined,
			// but if it's another error, we can call toString() on it too.
			if !cause.Get("toString").IsUndefined() {
				errMsg += ": " + cause.Call("toString").String()
			} else if cause.Type() == js.TypeString {
				errMsg += ": " + cause.String()
			}
		}
		errCh <- fmt.Errorf("net/http: fetch() failed: %s", errMsg)
		return nil
	})

	fetchPromise.Call("then", success, failure)
	select {
	case <-req.Context().Done():
		if !ac.IsUndefined() {
			// Abort the Fetch request.
			ac.Call("abort")
		}
		return nil, req.Context().Err()
	case resp := <-respCh:
		return resp, nil
	case err := <-errCh:
		return nil, err
	}
}

var errClosed = errors.New("net/http: reader is closed")

// streamReader implements an io.ReadCloser wrapper for ReadableStream.
// See https://fetch.spec.whatwg.org/#readablestream for more information.
type streamReader struct {
	pending []byte
	stream  js.Value
	err     error // sticky read error
}

func (r *streamReader) Read(p []byte) (n int, err error) {
	if r.err != nil {
		return 0, r.err
	}
	if len(r.pending) == 0 {
		var (
			bCh   = make(chan []byte, 1)
			errCh = make(chan error, 1)
		)
		success := js.FuncOf(func(this js.Value, args []js.Value) interface{} {
			result := args[0]
			if result.Get("done").Bool() {
				errCh <- io.EOF
				return nil
			}
			value := make([]byte, result.Get("value").Get("byteLength").Int())
			js.CopyBytesToGo(value, result.Get("value"))
			bCh <- value
			return nil
		})
		defer success.Release()
		failure := js.FuncOf(func(this js.Value, args []js.Value) interface{} {
			// Assumes it's a TypeError. See
			// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError
			// for more information on this type. See
			// https://streams.spec.whatwg.org/#byob-reader-read for the spec on
			// the read method.
			errCh <- errors.New(args[0].Get("message").String())
			return nil
		})
		defer failure.Release()
		r.stream.Call("read").Call("then", success, failure)
		select {
		case b := <-bCh:
			r.pending = b
		case err := <-errCh:
			r.err = err
			return 0, err
		}
	}
	n = copy(p, r.pending)
	r.pending = r.pending[n:]
	return n, nil
}

func (r *streamReader) Close() error {
	// This ignores any error returned from cancel method. So far, I did not encounter any concrete
	// situation where reporting the error is meaningful. Most users ignore error from resp.Body.Close().
	// If there's a need to report error here, it can be implemented and tested when that need comes up.
	r.stream.Call("cancel")
	if r.err == nil {
		r.err = errClosed
	}
	return nil
}

// arrayReader implements an io.ReadCloser wrapper for ArrayBuffer.
// https://developer.mozilla.org/en-US/docs/Web/API/Body/arrayBuffer.
type arrayReader struct {
	arrayPromise js.Value
	pending      []byte
	read         bool
	err          error // sticky read error
}

func (r *arrayReader) Read(p []byte) (n int, err error) {
	if r.err != nil {
		return 0, r.err
	}
	if !r.read {
		r.read = true
		var (
			bCh   = make(chan []byte, 1)
			errCh = make(chan error, 1)
		)
		success := js.FuncOf(func(this js.Value, args []js.Value) interface{} {
			// Wrap the input ArrayBuffer with a Uint8Array
			uint8arrayWrapper := uint8Array.New(args[0])
			value := make([]byte, uint8arrayWrapper.Get("byteLength").Int())
			js.CopyBytesToGo(value, uint8arrayWrapper)
			bCh <- value
			return nil
		})
		defer success.Release()
		failure := js.FuncOf(func(this js.Value, args []js.Value) interface{} {
			// Assumes it's a TypeError. See
			// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError
			// for more information on this type.
			// See https://fetch.spec.whatwg.org/#concept-body-consume-body for reasons this might error.
			errCh <- errors.New(args[0].Get("message").String())
			return nil
		})
		defer failure.Release()
		r.arrayPromise.Call("then", success, failure)
		select {
		case b := <-bCh:
			r.pending = b
		case err := <-errCh:
			return 0, err
		}
	}
	if len(r.pending) == 0 {
		return 0, io.EOF
	}
	n = copy(p, r.pending)
	r.pending = r.pending[n:]
	return n, nil
}

func (r *arrayReader) Close() error {
	if r.err == nil {
		r.err = errClosed
	}
	return nil
}